Bio-pesticides

Food security and environmental stewardship are two subjects on the minds of most individuals involved with agriculture. The misuse of conventional pesticides, in many cases, has led to pest resistance, population resurgence and pesticide residues. Once a novel idea with limited opportunities for use, biopesticides rapidly are becoming more widely available and represent an effective, environmental-friendly alternative method of pest control.

The term ‘biopesticide’ is a contraction of ‘biological’ (meaning living or involving life) and ‘pesticide’ (a substance or mixture of substances used to control pests). According to the Environmental Protection Agency (EPA), the term refers to “certain types of pesticides derived from such natural materials as animals, plants, bacteria, and certain minerals.” Biopesticides are considered to be forms of biological control. The latter includes the use of predators, parasitoides, pathogens and compounds of biological origin to control pests.

A familiar example of a biopesticide is the soil-derived bacterium Bacillus thuringiensis(or Bt). The latter frequently is used to control insect pests such as corn earworm and bagworm. Bt (e.g. Dipel®) is an effective insecticide because of a toxic crystal protein it produces. In the (alkaline) gut of an insect, the toxin is liberated from the crystals and paralyzes the digestive system of the insect. The end result is the insect stops eating and starves to death. Since the digestive system of mammals is acidic in nature, Bt is considered to be nontoxic to humans.

It must be emphasized that just because an organism or compound occurs in natures does not mean it is non-toxic. For example, nicotine sulfate (e.g. Black Leaf 40) is a derivative of tobacco that, for decades, was used as an insecticide to control pests such as aphids. Because of its high toxicity, it was removed from the market and is no longer available. Fortunately, a common denominator and attractive feature of most of today’s biopesticides is their low mammalian toxicity.

Biopesticides are normally placed in one of three categories:

1. Biochemical pesticides are naturally occurring, non-toxic pest controllers. Biopesticides belonging to this category include insect pheromones, natural plant and insect regulators, enzymes and bio repellents or attractants.

As an example, neem (Azadirachta indica) is an evergreen tree native to India. An oil pressed from the fruits and seeds of this tree contains, in addition to other insecticidal and fungicidal compounds, azadirachtin. The latter acts as an antifeedant and growth disruptor for more than 200 species of insects. Examples of biopesticides containing azadirachtin include Azatin XL® and Azaguard®. Both carry EPA labels for the control of many insect pests but are relatively non-toxic to mammals.

Additional examples of biochemical pesticides include BacStop™ (a mixture of herbs and oils derived from herbs) broadly labeled for the control of bacterial and fungal diseases; Organocide™ (5% sesame oil) labeled for both fungal diseases and insect control; and Regalia® an extract of giant knotweed (Reynoutria sachalinensis) useful in helping to make treated plants more resistant to certain diseases.

2. Microbial pesticides contain a micro-organism (e.g. bacterium, fungus, virus or protozoa) or a product derived from micro-organisms that controls pests. Dipel® (mentioned above) is an example of a microbial pesticide as is Grandevo®. The latter is a microbial insecticide/miticide containing the bacterium Chromobacterium subtsugae and solids derived from its fermentation. It has multiple effects on pests, including fecundity reduction, serving to deter feeding and acting as a stomach poison. It is labelled for the control of a wide array of insects on many different food crops commonly grown in the garden.

Other examples of microbial pesticides include Actinovate AG® (Streptomyces lydicus) for suppressing several foliar and soil-borne diseases; Cease® and Senerade® (different strains of Bacillus subtilis) useful for the control of a number of different disease on vegetables; and NOLO Bait™ (Nomesa lacustae) a microsporidium protozoan labelled for the control of over 90 species of grasshoppers, crickets and locusts. 

3. Plant-incorporated protectants are substances produced naturally by a plant. However, the gene(s) responsible for the production of these substances has been introduced to the genome of the plant via genetic engineering.

As an example, the gene in Bt responsible for the manufacture of the toxic crystal protein has been introduced into the genetic makeup of corn via genetic engineering. Bt corn, therefore, has the ability to make its own pesticidal protein, negating the need to apply the bacterium artificially. The EPA regulates the protein and the gene that produces it, but not the plant itself.

There are a number of advantages for using biopesticides.

First, they usually are inherently less toxic to humans than conventional, synthetic pesticides. However, proper precautions still need to be taken when using them. Always read and follow label directions.

Secondly, biopesticides have a fairly narrow toxicity range. They tend to affect only the target pest and closely-related organisms. Contrast this with the broad-spectrum activity common to many conventional pesticides. Therefore, biopesticides pose little risk to mammals, birds and beneficial insects.

Third, biopesticides often are effective at (relatively) low concentrations and usually degrade rapidly. The latter helps to lower exposures and to avoid environmental problems caused by conventional pesticides. Since they pose less risk to the environment, the EPA usually requires much less data (and time) to register a biopesticide, compared to the registration process for a conventional pesticide.

Finally, biopesticides fit well into Integrated Pest Management (IPM) programs. Properly used, they can greatly reduce the use of conventional pesticides, while promoting high crop yields because of effective pest control. On the negative side, biopesticides usually are more expensive than synthetic pesticides. It must be pointed out, however, that fewer applications normally are required. Additionally, in most cases pest control takes longer, given most biopesticides have little “knock down” activity. Therefore, preventative application is important.

Resource:

http://www.ipm.missouri.edu

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